It’s hot as hell in here. No, really, Gary Oldman has set the thermostat so high that it feels less like a room at the Beverly Hills Four Seasons than a fire-heated Transylvanian castle on a snow-blown mountainside.

“The first thing I do when I get into a hotel room is crank it up to about 80,” he says jokingly through that recognizable twangy British accent to a publicist as she makes her way out of the room. Or is it recognizable? Oldman is a classic character actor, a “that guy” for film-goers the world over. So maybe it is. But his career never took hold in a leading man capacity, so he lingers on the pages of recent film history. Maybe it was the dust-up behind the scenes over the perspective of Rod Lurie’s “The Contender” in 2000 that held him back at a time when his career was set to take off. Maybe that’s an overstatement.

He looks remarkably young. At 53, he’s taken on roles as of late that have played up older, wiser traits, but they’ve clearly shielded some vitality. His latest, Tomas Alfredson’s “Tinker, Tailor, Soldier, Spy,” is a prime example, Oldman saddling up to the role that Alec Guiness first fleshed out on the screen via British television mini-series. Now he’s being asked by young press types who aren’t likely aware of Guiness outside of “Star Wars” whether he was familiar with that project before taking the role.

Alas, Oldman’s status as a featured element of countless films that speak to young film enthusiasts (“Sid and Nancy,” “JFK,” “True Romance,” “León,” “Basquiat,” “The Fifth Element,” etc., etc.), coupled with his high profile gig in Christopher Nolan’s Batman franchise, has brought him to that place.

Since everyone’s asking, no, with “Tinker, Tailor, Soldier, Spy,” Oldman had no trepidation over taking on the John le Carré-penned role of George Smiley, regardless of who played it before him. It was a challenge and a unique one for the actor, who has made his name as a lively, outwardly performed slice of vast esteemed ensembles. Now he’s fronting one, but with a more subdued, inwardly performed piece of work. The irony is delicious.

“You take inspiration from anywhere, really, any way you can get it,” Oldman says of his approach to preparing for a role. “But with this, you are blessed in as much that you”re working from a great book. All the secrets, all the keys to unlocking the doors are all there in the book.”

Indeed, Oldman met with le Carré (the pen-name of author David John Moore Cornwell, who was himself a part of MI5, the British intelligence organization depicted in “Tinker, Tailor, Soldier, Spy”). He wanted to get a sense of who Smiley was before the audience meets him in the story, as it picks up much later in his career. What was he like as a younger man, when he was out on active service? Oldman quizzed le Carré for these particulars as flavoring for his performance.

“The most interesting thing we talked about, I think, was just the sheer level of paranoia,” Oldman says, “and the pressure one is under when you have an alias, when you”re undercover, and the fear that your cover will always be blown.”

That seems like the kind of thing that would greatly inform the physicality of the performance. So much of the film is observational, both (rather brilliantly) in theme and in atmosphere. The subtleties are a playground for an actor like Oldman.

“There”s a passage in the book that I will butcher,” he recalls, “but it is by Ann, George”s wife, who describes him as a creature that can regulate his sort of body temperature to that of the surroundings, almost like a reptile. And that suggested to me someone who is very still and not frenetic or fussy. I don”t see him as someone who”s touching himself all the time. [He mimics straightening his clothing.] There”s this sort of poise to it. So that gave me a clue. And, you know, we grayed the hair and there”s a slight hunch in the shoulders. You have to absorb the character. You’re always looking for the minutiae of things, how a character moves, how he walks, how he eats. And some characters are easier.”

It’s interesting Oldman would highlight Smiley as adaptable to surroundings and “almost like a reptile,” because Oldman himself has been described as a chameleonic actor. As noted in yesterday’s look back at his finest performances, he has settled into an array of characters with equal confidence and ease. But for the more nuanced Smiley, Oldman actually says the task at hand was easier than some of those embossed characters from his portfolio.

“Your life is the book, in a way,” he says. “The subtext. So you can always bring the book, even to a scene that has three lines and a look. I may have three lines and just a little flick of the eye, but you never felt that you were out there like a cork on the water, you know what I mean? You felt supported by the novel.”

The difference between “Tinker, Tailor, Soldier, Spy” and so many of those other movies is Oldman was able to marinate in the role. The flip-side is something like, say, Nolan’s Batman franchise, coming in, working a day and then being off for a month before coming back, working a week, and then having three weeks off, etc. The stop-and-go nature of filmmaking can play havoc on embodying a character and keeping it alive, so on this project, he was happy to let other actors, like Mark Strong or Colin Firth or Tom Hardy — all brilliant in the film — deal with those travails.

“When you”re asked to come in and you’ve got to burn from the first bar, it”s like rock and roll,” he says. “You’ve got to hit a frequency in a performance. And it may be violent, it may be emotional, it may be both. It may be tears. It could be many things. I always felt that as exciting as it was, there was a bit of a black cloud over me. You”d get there in the morning and it was like standing at the foot of a mountain looking at the peak and thinking, ‘Oh God, I”ve got to get there today, and when I call on it, will I have the resource? Is the well going to be dry or am I going to climb the mountain?’

“With Smiley, a lot of that sort of emotional work, in a way, was done in the privacy of my own home. It”s sort of done in my kitchen, me in a communion with the novel. And so it was a relief to know that it was other people that were bouncing off the wall and that I could come in and put my suit on and sit in a chair and listen. It was a great relief to be able to do that. There’s a continuity to it. And it”s those other guys that have to kind of come in and win the race, you know? Like I said, it”s like jazz. You just find that you ease into the solo and these other guys can start to come in and rock and roll.”

It’s left to be seen if Alfredson’s film is the one that brings Oldman his long-overdue first Oscar nomination. But how ironic would it be to come for an effort so of a piece with his work across an array of ensembles, yet so unique for the measured, reserved portrayal at its center?

“Tinker, Tailor, Soldier, Spy” opens in theaters nationwide Friday, December 9.

For year-round entertainment news and awards season commentary follow @kristapley on Twitter.

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